In the past, radiation images such as X-ray images have been widely used for diagnosing disease in clinical practice. Specifically, over a long period of history, radiation images formed via an intensifying screen-film system have accomplished high sensitivity and high image quality, whereby they are still utilized in clinical practice all over the world as an imaging system exhibiting high reliability and excellent cost performance at the same time. However, since the above-described image information is so-called analogue image information, and neither free image processing nor instantaneous electric transmission can be made in the similar way as in digital image information having been in progress in recent years.
Further, in recent years, a digital system radiation image detector, typified by computed radiography (CR) or the like has appeared. Since direct formation of digital radiation images is obtained by these and images can be directly displayed on an image display device such as a cathode tube, a liquid crystal panel or the like, the images are not necessarily formed on a photographic film. As a result, the above-described digital system X-ray image detector has reduced the need of image formation via a silver halide photographic system, and has significantly improved convenience of diagnostic action in hospitals and clinics. This computed radiography (CR) has been accepted at present in clinical practice, but not only sharpness is insufficient, but also space resolution is insufficient, whereby it has not achieved the same level as in a screen•film system.
On the other hand, further, a flat panel type radiation image detector (Flat Panel Detector: FPD) fitted with thin-film transistor (TFT) has been developed, for example, as a new digital X-ray image technology.
A scintillator panel made from X-ray phosphor exhibiting an emissive property produced by radiation in this flat panel type radiation image detector to convert radiation into visible light, but the use of a scintillator panel exhibiting high emission efficiency should be used in order to improve an SN ratio in radiography at a low dose. Generally, the emission efficiency of a scintillator panel depends on thickness of a phosphor layer (scintillator panel layer) and X-ray absorbance of the phosphor, but a thicker phosphor layer causes more scattering of luminescent light within the phosphor layer, resulting in lowered sharpness. Accordingly, sharpness desired for image quality determines the layer thickness.
Specifically, since cesium iodide (CsI) exhibits a relatively high conversion ratio of from X-rays to visible light, and a columnar crystal structure of the phosphor can readily be formed through vapor deposition, light guide effect inhibits scattering of luminescent light within the crystal, enabling an increase of the phosphor layer thickness.
However, since in the case of use of CsI alone, emission efficiency is low, one in which a mixture of CsI with sodium iodide (NaI) at any mixing ratio is deposited on a substrate via evaporation as sodium-activated cesium iodide (CsI:Na), or recently, one in which a mixture of CsI with thallium iodide (TlI) at any mixing ratio is deposited on a substrate via evaporation as thallium-activated cesium iodide (CsI:Tl) is subjected to annealing as a post-treatment to improve visible conversion efficiency, and the resulting is used as an X-ray phosphor.
As a method of manufacturing a scintillator panel, known is a method of forming a phosphor on a support such as an aluminum plate, an amorphous carbon plate or the like. In the case of the method of manufacturing a scintillator panel, it is generally known that deposited phosphor crystals caused by defects, dust and so forth on the support are anomaly grown, whereby protrusions are generated on the phosphor surface. Since such protrusions cause image defects, this should be improved.
As to the protrusions generated on such a phosphor surface, known are techniques of planarizing protrusions by squashing them with a jig, grinding them with a grinder for removal, cutting them with a cutting means, or the like (refer to Patent Document 1, for example).